1. Field of the Invention
This invention relates to a coaxial cable that includes an electric conductor, an insulating layer formed on a periphery of the electric conductor, and a conductive layer formed on a periphery of the insulating layer. In particular, this invention relates to a thin coaxial cable that uses a metallic nanoparticle paste as the conductive layer.
2. Description of the Related Art
As shown in FIG. 3, generally, a coaxial cable 30 includes a center conductor (electric conductor) 31, an insulating cover layer 32 (insulating layer) 32 formed on a periphery of the center conductor 31, and a shield layer (conductive layer) 33 formed as an outer conductor by winding a metallic wire or a metallic film around a periphery of the insulating layer 32, however, the method of forming the conductive layer 33 by the winding work has a problem that as a cable diameter becomes small, the fabrication becomes difficult.
Consequently, a method using a wet plating and a method using a conductive nanopaste that are superior to mass productivity even if the cable diameter is small, are proposed. For example, the former is disclosed in JP-1994(H06)-187847 and the latter is disclosed in JP-2006-294528.
The method using a conductive nanopaste is a method that forms the conductive layer on a periphery of a fluorine resin being a low dielectric resin by using a metallic nanopaste, and it can be described as an effective method for fabricating a thin coaxial cable.
However, the coaxial cable fabricated by the method using the conductive nanopaste has a problem that if a slight external deformation such as a bending occurs, an adhesion property between an insulating material forming the insulating layer and a metal thin film forming the conductive layer deteriorates so that the metal thin film are separated from the insulating material, and if the separation occurs, the film is broken, so that conduction of the external conductor becomes insufficient and a shield property is lowered. Also, in order to improve an adhesion property of the fluorine resin, a method using a chemical etching and a physical etching is known, however, it has a problem that process becomes complicated, cost of equipment becomes enlarged and waste liquid treatment becomes needed, so that mass productivity becomes insufficient.